Always collect static icons for all segments (#68712)
### What
Collect static metadata icons from the most leaf node in the component
tree, and then add them into resolved metadata icons if there's no icons
presented in exported metadata
### Why
Previously we collected the icons from the last item from collected
metadata items as last segment in the tree. But it doesn't act like that
when there's parallel routes, so we collect the last presented static
metadata icons from the metadata item list and then merge into the
resolved metadata at the end.
Fixes #68650
